Intercommunicating apparatus



Nov. 14, 1950 R. H. CAMPBELL INTERCOMMUNICATING APPARATUS Filed Aug. 15, 1947 Patented Nov. 14, 1950 IN TERCOMIMUNICATING APPARATUS Richard H. Campbell, Racine, Wis., assignor to Webster Electric Company, Racine, Wis., a corporation of Delaware Application August 13, 1947, Serial No. 768,367

Claims. l

, The vpresent invention relates to communicationapparatus and Vmore particularly to intercommunicating apparatus.

-The primary object of the present invention isv` to provide new and improved communication apparatus including at least one station of the master type comprising communication direction controlling switch means and one or more remote or speaker stations in which the master station is prevented from listening in on the remote stations without the latters knowledge. In other words, the apparatus is so constructed and arranged as to assure absolute privacy to the remote stations.

A further Aand morespecic object of the invention is the provision of new and improved apparatus ofthe character described in the preceding paragraph including an amplifier and a silencing relay controlling the operativeness of the amplifier which is under the conjoint control of the communication direction controlling switch means at the master station and a control switch at the Vremote stations, the control being so constructed and arranged that the relay cannot be operated to render the ampliier inoperative when the apparatus is conditioned for transmission from the master to the remote station and that the relay cannot be operated to render the amplifier operative when the apparatus is conditioned for transmission from the remote to the master station except'under the control of a person at the remote station.

vA .further object ofthe present invention is to provide a new and improved apparatus of the4 character set forth above, which includes, in addition, means for enabling the remote stations to originate calls. Y

, The apparatus of this invention is particularly well adapted for use in nurses homes, hotels, dormitories, schools, oflice suites, and institutions, all of these being places wherein privacy is desired. Other objects and advantagesof the present invention will become apparent from the ensuing description of an embodiment of the invention, in the course of which reference is had to the accompanying drawings, the single figure of which illustrates diagrammatically communication apparatus constructed and arranged in accordance with the present invention.

Referring now to the Vdrawing, there is illustrated an intercommunication system, of the loud speaking type, wherein communication may be carried on between a lirst station, called a master station, and one or more remote or substations under the control of communication direction controlling switch means at the master station.

The master station is indicated by the reference character I and two of a number of substations are indicated by the reference characters 2 and 3. The stations are provided with translating devices capable of being used both as receivers and transmitters, these being the loud speakers II, I2 and I3 at the three stations, respectively, which may be of the well known permanent magnet type. v

The master station is provided with an ampliiier 2B, a combined communication direction and power control switch 2|, and station selector switches 22 and 23 individual to stations 2 and 3, respectively. The amplifier may be of any well known construction and it will not be described in detail further than is necessary for an understanding of the present invention. In brief, it'

comprises an input transformer 24 andan output transformer 25 coupled by a pair of grid controlled tubes 26 and 2l.

In accordance with one of the features of the present invention, theoperativene'ss of theamplilier is controlled in such a way that the master station is prevented from listening in on the remote stationsv 2 and 3 without the knowledge and consent of the latter. The operativeness is controlled by means including a conductor v28 through which the grid 29 of tube 21 is grounded to' render the amplifier inoperative. The ground circuit is completed' through the conductor 28, a switch 30 biased to a normally open position, a conductor 32 connected to a common ground conductor 34. It may be well at this point briefly to refer to the fact that the switch 30 is operated by a coil 36, the latter being effective to close the switch when energized, and that the coil and switch together constitute what may be termed -a silencing relay.

YPower is supplied to the amplifier from a suitable source of alternating current through power supply means indicated generally by the reference character 40 and comprising a rectifier tube 42 through which plate voltage is supplied to the tubes and a ilament secondary winding 44 through which power is supplied to the filaments of the tubes26 and 2l in known manner. The plate voltage supply means includes a secondary winding 46, the midpointof which is connected by conductor 48 to the common ground conductor 34. The other side of the plate voltage supply includes a conductor 50, from which connections lead to the power and communication direction 3 control switch and the relay winding 36, as will be described in detail shortly.

The power and communication direction control switch 2| is of the three position type. In its indicated middle position, it occupies what is called a listen position in which the loud speaker l l is connected to the output transformer 25, and a communication-circuit comprising conductors 52 and 54 is connected to the input transformer 24. In its lowermost position, the switch 2| occupies what is called a talk position, in which the connections of loud speaker :arid the line 52, 54 are reversed. In its uppermost position, the

loud speaker l! is connected directly tothe linev 52, 54. In the talk and listen positionsthe plate voltage supply circuit is completed, but in the talk position the relay coil 36 cannot be energized because the supply voltage is shorted out so that the amplifier cannot be rendered inoperative'and the master station can call the remote stations.

` The connections of the loud speaker and the circuit 52, 54 are controlled by switch blades 56, 58, 66, 52 and 64 ofthe switch 2|. I n the listen position of the switchfline 52, 54 is connected vto the "input transformer of the amplifier through the switch bladesv 58* and 64 and conductors 66 and 68. At the same time, loud speaker I! is connected to the output transformer through coducters l :and 12,,s`w'itch blades 56 and 62 and conductors 'I4 and 16, In the talk position, the connections ofthe loud speaker and line are reversed, the loud speaker bein-g connected to the inputfcircuit through the Vswitch blades 56 and '62 and lines 52V and 54fbeing connected to the output transformer through switch blades 58 and 64. In the idle position of the switch, loud speaker H is connected ydirectlyto line 52, 544through the switch blades 58 and 64.

Plate voltageis 'supplied to the amplier'in the listen'A 'andtalk' positions of switchZl vby means including switch bladel and'co'nductors and v82 which are connected to 'conductor 50 and a lter 84 through which voltage is supplied to the plates of tubes 26V Vand 21fin known manner. In the third or idle-position, no plate'voltag'e :is supplied to the tubes.

In accordance with the present invention, the operativeness of the amplier is so controlled that station l `cannot listen inor eavesdrop on the remote stations 2 and 3 without the'knowledge of the latter. The remote 'stations are Vprovided with'control means operable to render the amplifier operative so `that communication may be had from the remote stations to the' master station. TheV arrangement-us also Vsuch that the master station can call -or talk to the remote stations at any time.

The amplifier operativeness controlling means includes, as '.alreadyindicated, the-silencing relay comprisingl switch 36 and coil 36. The coil isso controlled that it is energized to close switch 3!! andvthereby 'to' render the amplifier inoperative by grounding the. grid 29 of tube 21 whenever the communication direction control switch 2| is in its indicated listen position and a remote station isselected and the previously referred to control switch at the remote station is in its normal position. Further, the control is such that the coil 36 ris prevented from being energized when the switch 2 4|V is operated to its talk position.

, The coil is connected to the plate voltage supplying means through a voltage divider comprising-the series connected resistors el) and 92,'the former of which is connected by conductor 94 to conductor 56 and the latter of which is connected to the ground conductor 34. The resistors @fre shunted by a filter capacitor` 96. The coil is con-` nected to the junction of resistors 96 and 92 by a conductor 98 and under certain `conditions is energized by the voltage drop across resistor 92. The coil is also connected by conductor |60 to the junction of resistors |02 and |64 which are connected in series across the ,communication line 52, 54 throughwhich a control circuitforethe coil is extended to the remote stations 2 andv 3.

The remote stations 2 and 3 are each provided with a control switch |06 so constructed and arranged in circuit' that in one position it completes an energizing circuit for the coil 36 should the master station attempt to listen in on the remote staton and thus renders the amplifier inoperative. AssumingI that station desires to listen in on stationl 2, then selector switch 22 is closed. The coil 36 is then connected to the remote station zthrough conductor |66, the resistors |02 and |04, circuit 52, 54, switch 22, the pair of interstation conductors |68, resistors |||l and H2 at the ren mote station connected in series across conductors |68, the control switch IE6 connected to the junction of the resistors, and the common ground connector 34. This circuit connects the coil' 36 across the resistor 92 with the result that'it-is y energized and closes switch 3|), thereby rendering the amplier 2-6 inoperative and making it impossible for station i to listen in to station without the knowledge and consent of the latter. However, station I can listen to station 2 when the switch |66 is moved to its other position wherein theI energizing circuit ffo'r coil? 3'6 l is"b1"'o ken. As soon as this circuit is broken the switch 3D is returned to itsopen position, thereby rendering the amplifier operative.

The apparatus at station 3 is rlike that at' station 2 and will, therefore, v'not be described, although like parts will be indicated by like-reference characters.

The remote stations are also 'provided with means for calling the-'master station. This means includes a switch |-|4 movable from anormal open circuit positionto a circuit closing position in which a circuit is completed between conductors ||6-|2 or |'I6-I3, and 34. When either of these circuits is closed, a visual indicator operating coil ||8 individual to the calling station is energized as is-a "common buzzer |20. 'The'energizing circuit is completed rthrough a resistor |22, the secondary winding 44 and a conductor |24.

The master station can call a remote station at any time. To accomplish this, the switch 21 is provided with a switch blade |26 for shorting resistor 92v in the talk positionso thatthe coil cannot be energized 'to lrender the `amplifier inoperative.l The coil is snor-ted `through a circuit including the 'switch and conductorsl 'I 28 and |36. y

In oper-ation, fthe yapparalt-'us'is -suppliedwithenergy from a convenient source, such as the-ordinary 110-volt power supply lines. The rectifier 40 is immediately placed in operation t0 supply plate voltage andthe tubes are all conditioned for operation. The plate Voltage supply for the tubes is completed by -the Aswitch* blade-18 through 'the conductors and 82, provided switchv 2| is in its indicated position. The'silencing relay is "in its indicated position 'so that the amplifier vis operative. The loud speaker `at the master station 'is 'connected'tothe output of the" amplifier and the communication line 52, `54 isV connected to the input.

Assuming that the master 'station desires to 'listenin to one of the remote stations, say station 2, then the selector switch 22 must be closed. Whenlthis': is done, the coil 36 is energized to lrenderthe amplier inoperative by closing switch l30r and grounding the input circuit for amplifier tube 21. It is thusimpossible for the master .station to listen in on a substation.

Should the master station desire to call station 2 it is necessary only that the selector switch 22 `vbevclosed and switch 2| be operated into its lovvermost or bottom position. In this position, .plate voltage continues to be supplied to the amplifier through theswitch blade 'I8 and conducltors-,and 82, but coil 36 is prevented from operatingswitch 30 to render the amplifier inoperative because voltage supply resistor 92 is shortved, vas earlier described. Consequently, the master station can call the remote station, it being 'remembered that in the talk position the loud Aspeaker I I is connected t0 the amplifier input and v-the output is connected to line 52, 54 and thence through the interstation conductor |08 to the loud speaker |2.-

In order to respond to a call, the remote sta- 'tion must open switch |66, while the master station releases switch 2| for return to its listen position. With the switch |06 opened and switch 2| in its listen position, the coil 36 is not energized, so that the amplifier is operative, and -loud vspeakers I2 and are connected to the input and output of the amplifier, respectively.

Should the master station try to listen to some -other remote station, such as station 3 when lisxtening t0 station 2, whereat switch |56 is open, the amplifier is rendered inoperative because an energizing circuit for solenoid 36 would be completed through switch |06 at station 3.

"Should a remote station desire to call the master station, the switch blade I4 at the former `is closed, thereby to operate the visual and audible indicating means I8 and |20. To reply, the .master station closes the selector switch corresponding to the calling station and calls the re- -mote station and the latter then opens switch |06 thereat to condition the apparatus for twoway." communication .under control of switch 2| at the master station.

From the foregoing description of the present invention, it may be noted that it is impossible for the master station to listen in to a remote station without knowledge and consent of the latter and that this result is obtained through a simple circuit arrangement including, in the main, a single relay conjointly controlled by control means at the master and remote stations. The arrangement is also characterized by being silent :in operation and in that but low voltage current need be handled by the silencing relay switch.

While the invention has been described in connection with the details of a single embodiment thereof, it should be understoody that these details are not intended to be limitative of the invention, except in so far as setforth in the accompanying claims. r

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. Communication apparatus including an amplifier, a device usable both as a receiver and a transmitter, means including a communication control switch for selectively connecting said device to the input or output of said amplifier and energizing the amplifier to render it operative, means including a relay controlled by said cornmunication control switch for. controlling `the operativeness of the energized amplifier, a second device usable as a receiver and transmitter, and means including switch means located in proximity to said second device controlling said relay for also controlling the operativeness of theenergized amplifier.

2. Communication apparatus including an amplier, a device usable both as a receiver and a transmitter, means including a communication control switch movable to talk and listen positions for selectively connecting said device to the input or output of said amplifier and energizing the amplifier to render it operative, meansincluding a relay operable to render the energized amplifier inoperative, a second device usable as a receiver and transmitter, means including switch means located in proximity to said second device controlling said relay for rendering it effective to render the energized amplifier inoperative, and means including switch means operable by said communication control switch in its talk position for preventing said first mentioned switch means from rendering said amplifier inoperative.

3, Communication apparatus including an amplier, a device usable both as a lreceiver and a transmitter, means including a communication control switch movable to listen and talk positions for selectively connecting said device to the input or output of said amplifier and energizing the amplifier to render it operative, means including a relay operable to render the energized amplifier inoperative, a second device usable as a receiver and transmitter, means including selector switch means at the first station and switch means located in proximity to said sec- 'ond device controlling said relay for rendering it effective to render the energized amplifier inoperative, and means including 'switch `means operable by said communication control switch in its talk position for preventing said rst mentioned switch means from operating said relay and rendering said amplier inoperative.

4. Communication apparatus including an amplifier including a grid controlled tube, a device `usable both as a receiver and a transmitter,

means including a communication control switch movable to listen and talk positions for selective- 'ly connecting said device to the input or output of said amplifier, means including a relay comprising a switch operable upon energization of said relay to ground the grid of said tube for vrendering vsaid amplifier inoperative, a second device usable as a receiver and transmitter, means including switch means located in proximity to said second device for energizing the relay and operating the switch to ground said `gri'd'and' thereby to render said amplifier inoperative, and means including switch means In vcoinniimication apparatus, amplifying meanafaiirst station including communication control switch means operable into talk and listen positions, amplifying means conditioned for operation, means including relay means controlling the operativeness of said amplifying means and operable to render said .amplifying means inoperative, a second station including switch means for operating said relay means, .and means operable by said control switch in its talk position for rendering said switch means ineffective to operate said relayV means.

7. In communication apparatus, a first Vstation having amplifying means including a grid controlled tube and means including aA relay comprising switch means controlling the vgrid circuit of .said tube for controlling the operativeness of said amplifying means and capable of rendering said amplifying means inoperative, and a second station having control switch means controlling saidV relay and `operable to operate said relay to render said amplifying means inoperative.

8-. In communication apparatus, a first station hav-ing kamplifying means including a grid controlled tube, means including a relay comprising switch means controlling lthe grid circuit of said tube for controlling the operativeness of said amplifying means and capable of rendering said amplifying means inoperative, and a station selector switch, a second station having a control switch anda Acircuit connecting it to said relay through said station selector switch controlling 'said relay and operable to operate said relay to render said amplifying means inoperative.

9. In communication apparatus, a first station having amplifying means including a grid controlled tube and means including a relay comprising switch means controlling the grid circuit of said tubefor controlling the operativeness of said `amplifying means and capable of rendering said amplifying means inoperative, a Ysecond station .having control 'switch means controlling said relay and operable to operate said relay to render said amplifying means inoperative, communication controlling 'switch means at the first station controlling said amplifying means and operable to condition the latter for transmission to the second station, and switch means operable by said communication Vcontrolling switch means and controlling said relay for preventing operation of said; relay by the control switch means at the lsecondl station.

10. -In communication apparatus, amplifying means, means' including va relay comprising switch means for controlling the operativeness of said amplifying means and operable to render said amplifying means in operative, plural position communication control switch means controlling communication circuit connections to said ampliiier, and means operable :by said control switch means inone of its positions for preventing operation of said relay to render said amplifying means inoperative.

11. In communication apparatus, amplifying means, means including a relay comprising switch means 'for'` controlling thev operativeness fof: said amplifying .means and operable to render fsaid amplifying means inoperative, communication controlswit'ch meansY having -talk 4and listen positionscontrolling :circuit connections to said' amplifier,` and meansoperable vby said control switch means in its talk position for preventingfoperation of said relay to render said amplifying means 3inoperative.

12. In communication apparatus, amplifying means, means including a normally deenergized but energiz'able relay comprising switch vmeans for controlling the operativeness' of said amplifying meansplural position communication control switch means controlling circuit connections to said amplifier, and means operable by said control' switch means in one of its positions vforxpreventing energi'zation of said relay.

13. In `'communication apparatus, amplifying means, means including a normally deenergized relay energizable to render said amplifying means inoperative, communication control switch means having talk and listen positionsand 'controlling circuit connections to said amplifier, `and'means operable by said control switch means in its talk position for preventing energization of said-relay and thus preventing said amplifying means from being rendered inoperative.

14. In communication apparatus, amplifying means, means including an energizable relay comprising switch means for controlling theA operativeness of said amplifying means, plurali position communication control switch means controlling circuit connections to said amplifiergother control switch means for energizing said 'relay means to render said amplifying meansinoperative, and means operableby said control switch means in one of its positions forpreventing *energization of said relay means.

l5. In communication apparatus, amplifying means, plate voltage supply means for said amplifying means, means including plural positionV REFERENCES CITED l N The ffollowing references are of record in the file .of this patent:

UNITED STATES PATENTS Number Narne Date 1,802,675 Sisty et al. f. Apr. 2.8, 1 931 2,269,141 Campbell v. Jan. 6, 1942 2,269,144 Campbell Jan. 6, 1942 2,377,672 Campbell a June 5, 1945 

